Cameras utilized in providing an image of a radioactive source are frequently composed of a scintillator crystal and a collimator for guiding radiant energy from the source to the scintillator crystal. An array of photomultipliers is positioned on the opposite side of the scintillator crystal for receiving flashes of light emitted by the crystal in response to the incident radiant energy. Typically, the measure of light energy received by each photomultiplier is obtained by integrating circuits coupled to each of the photomultipliers, the relative magnitudes of these energies serving to indicate the location of each of the light flashes on the crystal. The stored energy of each of the photomultipliers is converted to a signal suitable for combining with the signals obtained from the energies of the other photomultipliers. Weighting circuitry is utilized in the combining of these signals to provide points on a display, such as a cathode-ray tube display, which correspond to the points of illumination upon the scintillation crystal. A circuit having an electronic window frequently referred to as a pulse height analyzer, is utilized in the coupling of these signals from the photomultipliers to the display to ensure that only signals having an energy within a prescribed range of energies are coupled to the display.
A problem arises in that the photomultipliers are often placed close to the scintillator to maximize the resolution of the camera; however, the close spacing causes an increased density of signals on the display emanating from light flashes directly in front of a photomultiplier than from light flashes occurring to the side of the photomultiplier. As a result, a radiographic image appearing on the display has an appearance which is modified somewhat from the appearance of the subject due to the fact that there is a greater density of points on the display at positions corresponding to the positions of the photomultipliers in the array of the photomultipliers. There is an apparent visual effect perceived by an observer of the image which shows an outline of the array of photomultipliers superposed upon the image of the subject.